Myocardial fiber orientation undergoes an orderly transition from epicardium to endocardium in the left ventricle. In the anterior free wall of the left ventricle midwall fibers course in a general circumferential direction and fibers on the endocardium and epicardium are oriented longitudinally. At the apex and base of the heart fiber direction changes more rapidly and adjacent valve rings influence local myofiber direction. How fibers lying at different depths and locations in the myocardium interact to produce local deformation is not known. One theory holds that individual fibers act as slippery rods and exert no force on fibers lying at different directions in the heart wall. However, epicardial deformation is influenced by the function of other fiber layers, and loss of function of subendocardial fibers effects transmural function. It will be the general objective of these studies to define the relationship between fiber direction and local deformation. We propose to utilize high speed biplane X-ray and three rows of lead beads implanted across the left ventricular wall of anesthetized dogs. Assumptions of the infinitesimal theory of axisymmetric membranes will be avoided, and the more complete theory of finite deformation in three dimensions will be utilized. Measured transmural deformation expresses as principal strains in .5 gm tetrahedron of muscle will be compared to local fiber direction determined histologically. Studies will be conducted in the normal heart in the left ventricular free wall, in the septum, and near the apex and base where fiber direction changes rapidly. Moreover, studies are planned under conditions which have been shown to modify regional function (abnormal activation sequence, ischemia) and under chronic conditions where the left ventricle undergoes large changes in shape (volume or pressure overload hypertrophy). It is anticipated that these studies will provide significant insight into the relationship between anatomic arrangement of myofibers and local ventricular deformation in the normal and diseased heart.